Temperature Coefficients of Photovoltaic Devices

Abstract

This chapter introduces the concept of temperature coefficient which enables to quantify the temperature sensitivity of the performances of photovoltaic devices. The temperature sensitivity of a photovoltaic converter originates from the temperature dependence of the fundamental conversion losses and of the bandgap of the absorber. The detailed balance principle is used to derive the fundamental losses which set the maximum of photovoltaic conversion efficiency in the radiative limit. It is highlighted that the unusual temperature dependence of the bandgap of perovskite compounds will ultimately result in peculiar temperature sensitivities. Following the discussion on the fundamental losses, the additional losses limiting the efficiency of present commercial cells are considered. The different loss mechanisms that drive the temperature coefficients of important cell parameters (open-circuit voltage Voc, short-circuit current density Jsc, fill factor FF) are identified. The analysis shows how each of these temperature coefficients can provide some insight into device physics. The temperature sensitivity of open-circuit voltage is connected to the balance between generation and recombination of carriers and its variation with temperature. The temperature sensitivity of short-circuit current is driven by the bandgap temperature dependence and the incident spectrum on one hand and on the temperature dependence of the collection efficiency of the device on the other hand. As for the fill factor temperature sensitivity, it is ideally closely related to the open-circuit voltage temperature sensitivity but it also depends for certain devices on technological issues linked to carrier transport. The chapter ends with an overview of the possible approaches to tune the temperature coefficients of photovoltaic devices.